gateware.ripple: add support for a ripple counter, with external clock

Author: attie-argentum

software/glasgow/gateware/ripple.py

@@ -0,0 +1,30 @@
+import logging
+from nmigen import *
+
+__all__ = ["RippleCounter"]
+
+class RippleCounter(Elaboratable):
+    def __init__(self, clk, clk_en=None, rst=None, width=8, logger=None):
+        self.logger = logger or logging.getLogger(__name__)
+        self.clk    = clk
+        self.clk_en = clk_en
+        self.rst    = rst
+        self.width  = width
+        self.count  = Signal(width)
+
+    def elaborate(self, platform):
+        if not hasattr(platform, "get_ripple_ff_stage"):
+            raise NotImplementedError("No Ripple Counter support for platform")
+
+        m = Module()
+
+        clk_chain = self.clk
+
+        for i in range(self.width):
+            d_out = Signal()
+            clk_en = self.clk_en if i == 0 else None
+            m.submodules += platform.get_ripple_ff_stage(d_out, clk_chain, clk_en, self.rst)
+            m.d.comb += self.count[i].eq(d_out)
+            clk_chain = d_out
+
+        return m